LONDON—The U.K. agency that evaluates the cost-effectiveness of drugs has recommended that the English health system pay for the Sovaldi hepatitis C treatment sold by Gilead Sciences Inc., at a discount of roughly 30% from its U.S. price.

Separately, Gilead said Friday that it scored a key victory in securing the rights to Sovaldi, after a U.S. arbitration panel ruled in the company's favor over Roche's claims on the lucrative...